Error message at checkout

Customers are getting the following error message at checkout

A new entity was found through the relationship ‘MailPoetEntitiesSendingQueueEntity#task’ that was not configured to cascade persist operations for entity: MailPoetEntitiesScheduledTaskEntity@28466. To solve this issue: Either explicitly call EntityManager#persist() on this unknown entity or configure cascade persist this association in the mapping for example @ManyToOne(..,cascade={“persist”}). If you cannot find out which entity causes the problem implement ‘MailPoetEntitiesScheduledTaskEntity#__toString()’ to get a clue.

this only started today and is a handful of customers.

please help

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